Toll-like receptors (TLRs) and other pattern-recognition receptors (PRRs) form functional receptor complexes that recognize pathogen-associated molecular patterns (PAMPs). Activation of the TLR signaling pathway by PAMPs leads to induction of immune and inflammatory responses. Porphyromonas gingivalis is an important pathogen in human periodontitis, the pathogenesis of which derives mainly from untoward host inflammatory reactions to subgingival bacterial challenge. Periodontitis is a significant health problem in adults and may precipitate systemic complications such as atherosclerosis. A major cell surface component of P. gingivalis is the fimbriae, which function as an adhesin. Strikingly, fimbriae activate transcription factor NF-kappaB and induce production of proinflammatory cytokines through interactions with several PRRs. Understanding the molecular basis of how the host recognizes and responds to P. gingivalis fimbriae is essential for developing molecular approaches to control periodontal inflammation. Therefore, the objective of this proposal is to elucidate the proinflammatory interactions of fimbriae with PRRs. We hypothesize that fimbriae function as a PAMP and interact in a regulated mode, and through discrete epitopes, with different binding PRRs resulting in the activation of TLR signaling and induction of proinflammatory cytokines. Fimbrial epitopes involved in cellular binding and/or activation will be identified using fimbrial peptides and mutant fimbriae. Importantly, epitopes involved in binding but not activation may find application as antagonists of fimbria-induced inflammation. Our preliminary experiments have shown that TLR2 and TLR4 mediate fimbria-induced signaling, but initial recognition of fimbriae is mediated by cooperation between CD14 and CD11b/CD18, which thus appear to serve as TLR co-receptors. It is postulated that fimbriae initially bind to CD14, and the fimbriae/CD14 complex induces TLR2-mediated "inside-out" signaling that leads to activation of the ligand-binding capacity of CD11b/CD18. PRR-fimbriae interactions will be examined in human monocytes and mouse macrophages derived from normal and PRR-deficient mice. Elucidation of the mechanisms whereby PRRs recognize and respond to fimbriae and identification of flmbrial antagonists may facilitate the design of novel approaches to therapeutic intervention in both periodontitis and atherosclerosis, where P. gingivalis has also been implicated.